A fine-particle-dispersed polyol is used for the purpose of improving physical properties, for example, compressive hardness and durability, of a polyurethane foam, and is obtained by polymerizing an ethylenically unsaturated monomer in a polyol in the presence of a polymerization initiator. In recent years, a polyol in which fine particles having a small average particle diameter are dispersed has been demanded for the purpose of further improving mechanical properties such as elongation at break. Known methods to decrease the particle diameter include a method of increasing a ratio of acrylonitrile as a part of an ethylenically unsaturated monomer used (see Patent Document 1), which includes a process in which a seed dispersion composed of preliminarily formed submicron particles is prepared in polymerization in the first step, and a monomer is added to the seed dispersion and polymerized in the second step so that a desired polymer concentration is obtained. Still further, another method also is known in which a fine-particle-dispersed polyol is obtained by carrying out polymerization in the presence of, as an intermediate material, a seed dispersion with preliminarily-formed submicron particles dispersed therein, (see Patent Document 2).
Patent Document 1: JP 6(1994)-172462 A
Patent Document 2: JP 2005-526155 A (WO 03/097710 A1)